Canopy chatter
Occasionally during an aggressive spin entry or just wind up turns with an intentional accelerated stall, the canopies on the may have just enough play in the rollers / rails that they make a popping sound at the stall break. My 8 will do it some times if its a very aggressive stall break. I think the canopy is loaded in compression during most flight regimes, but when there is a sudden unloading, they might be moving just a bit. Another example of this is when I demo a power on stall in a 9A tip I fly, the canopy is nice and tight in flight, but hold it in a sustained buffet stall and the canopy will chatter against the latches. I mounted a go-pro on my 8 canopy during spin testing and it clearly showed a slight jump in the roller to rail junction during the break, even recorded the sound. Scared me silly until I figured out what it was. Did the same thing on a 6A during accelerate stall flight testing, but much more pronounced.
Your results and assumptions may vary from mine.